1. Field of the Invention
The present invention relates to a device to mitigate the response of solid fuel propellant motors when subjected to unwanted extraneous heating particularly, though not exclusively, under so-called "slow cookoff" conditions.
2. Discussion of Prior Art
Explosive materials when exposed to heat can react in various ways. Depending upon the nature of the explosive and the rate of heating, the two most common exothermic reactions of explosive materials are ignition and detonation. Desirably, an explosive substance should not react under any conditions other than those of its specific initiation procedure. Furthermore, it should not react either by ignition or detonation at relatively low temperatures of less than about 160.degree. C. However, this is seldom the case.
Explosive materials can be broadly divided into those which are intended to detonate and those which are intended to ignite or burn, albeit very rapidly. The present invention is mainly concerned with the latter type of material, an example of which is propellant material used for applications such as rocket motors.
Propellant materials, based for example on nitrocellulose (NC) or mixtures of nitrocellulose and nitroglycerine (NG), when subjected to extraneous heating at a relatively rapid rate will generally react by producing an ignition event where the material burns rather than detonates. The temperature at which this ignition event occurs is dependent on the heating rate of the material. A typical ignition temperature range for propellants based on cast NC/NG matrices is about 160 to 180.degree. C. at, for example, a heating rate of 5.degree. C. per minute. However, although undesired ignition of a propellant motor is a serious and dangerous event, the potentially more dangerous event of explosive detonation may occur when the material is subjected to a very low heating rate. A heating rate of about 0.05 .degree.C. per minute, for example, from ambient temperature may cause detonation at a temperature of about 120.degree. C.
During a detonation event, substantially all molecules of the material release their chemical energy simultaneously. A slow heating rate serves to bring the majority or all of the molecules in the motor matrix to an energy level where the next increment of heat input takes the material above an activation energy "barrier" to promote a simultaneous reaction causing a detonation event.